You can turn a character trait into a flaw to create emotion in the other characters and situations.

          You can list the weaknesses of all characters and add another abrasive character= or characters to exploit those weaknesses.

          You can add unexpected obstacles, physical or otherwise, and introduce interesting minor characters that may become protagonists in your next book or series.

          You can offer a new discovery that might change the goals and understandings. A caveat here is not to go overboard on this one especially if you have a well-planned-out ending.

          You can, however, suggest here uncertain outcomes and goals; although, this is done nowadays to flesh out too-short novels.

          You can play around with the settings or change them, which may work especially well in coming-of-age stories, as each setting offers new promises and challenges.

          Then, if you are really sure of yourself, you can create a subplot to add variety and extra information, such as a character learning a new skill that may have an effect on the main conflict.